What is the most important word to add to a Fixed Mindset statement in order to turn it into a Growth Mindset statement?

Answer: "yet"

People who have a "fixed mindset" tend to believe that they cannot change their personality or their abilities. This leads them to see effort and difficulty not as learning opportunities but just as inconveniences.

On the other hand, people with a "growth mindset" are convinced that hard work and discipline can lead them to develop better abilities. They do not only trust natural talent. They tend to put more effort into things, which leads them to achieve better outcomes.

The introduction of the word "yet" can turn an idea from a fixed mindset (I cannot speak Spanish) into one from a growth mindset (I cannot speak Spanish yet).